Magnetic resonance spectroscopic changes in Alzheimer's disease

Quantitative Assessment of Occipital Metabolic and Energetic Changes in Parkinson's Patients, Using In Vivo 31P MRS-Based Metabolic Imaging at 7T

Abnormal energy metabolism associated with mitochondrial dysfunction is thought to be a major contributor to the progression of neurodegenerative diseases such as Parkinson's disease (PD). Recent advancements in the field of magnetic resonance (MR) based metabolic imaging provide state-of-the-art technologies for non-invasively probing cerebral energy metabolism under various brain conditions. In this proof-of-principle clinical study, we employed quantitative ³¹P MR spectroscopy (MRS) imaging techniques to determine a constellation of metabolic and bioenergetic parameters, including cerebral adenosine triphosphate (ATP) and other phosphorous metabolite concentrations, intracellular pH and nicotinamide adenine dinucleotide (NAD) redox ratio, and ATP production rates in the occipital lobe of cognitive-normal PD patients, and then we compared them with age-sex matched healthy controls. Small but statistically significant differences in intracellular pH, NAD and ATP contents and ATPase enzyme activity between the two groups were detected, suggesting that subtle defects in energy metabolism and mitochondrial function are quantifiable before regional neurological deficits or pathogenesis begin to occur in these patients. Pilot data aiming to evaluate the bioenergetic effect of mitochondrial-protective bile acid, ursodeoxycholic acid (UDCA) were also obtained. These results collectively demonstrated that in vivo ³¹P MRS-based neuroimaging can non-invasively and quantitatively assess key metabolic-energetic metrics in the human brain. This provides an exciting opportunity to better understand neurodegenerative diseases, their progression and response to treatment.

Metabolic Dysregulation Contributes to the Progression of Alzheimer's Disease

Alzheimer's disease (AD) is an incurable neurodegenerative disease. Numerous studies have demonstrated a critical role for dysregulated glucose metabolism in its pathogenesis. In this review, we summarize metabolic alterations in aging brain and AD-related metabolic deficits associated with glucose metabolism dysregulation, glycolysis dysfunction, tricarboxylic acid (TCA) cycle, oxidative phosphorylation (OXPHOS) deficits, and pentose phosphate pathway impairment. Additionally, we discuss recent treatment strategies targeting metabolic defects in AD, including their limitations, in an effort to encourage the development of novel therapeutic strategies.

31 P T2 s of phosphomonoesters, phosphodiesters, and inorganic phosphate in the human brain at 7T

PURPOSE

To determine the phosphorus-31 T2 s of phosphomonoesters, phosphodiesters, and inorganic phosphate in the healthy human brain at 7T.

METHODS

A 3D chemical shift imaging multi-echo sequence with composite block pulses for refocusing was used to measure one free induction decay (FID) and seven full echoes with an echo spacing of 45 ms on the brain of nine healthy volunteers (age range 22-45 years; average age 27 ± 8 years). Spectral fitting was used to determine the change in metabolic signal amplitude with echo time.

RESULTS

The average apparent T2 s with their standard deviation were 202 ± 6 ms, 129 ± 6 ms, 86 ± 2 ms, 214 ± 10 ms, and 213 ± 11 ms for phosphoethanolamine, phosphocholine, inorganic phosphate, glycerophosphoethanolamine, and glycerophosphocholine, respectively.

CONCLUSION

The determined apparent T2 for phosphoethanolamine, glycerophosphocholine, and glycerophosphoethanolamine is approximately 200 ms. The lower apparent T2 value for phosphocholine is attributed to the overlap of this resonance with the 3-phosphorous resonance of 2,3-diphosphoglycerate from blood, with an apparent shorter T2 . Omitting the FID signal and the first echo of phosphocholine leads to a T2 of 182 ± 7 ms, whereas a biexponential analysis leads to 203 ± 4 ms. These values are more in line with phosphoethanolamine and the phosphodiesters. The short T2 of inorganic phosphate is subscribed to the fast reversible exchange with γ-adenosine triphosphate, which is mediated by glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase within the glycolytic pathway. Magn Reson Med 80:29-35, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Protective effects of 7,8-dihydroxyflavone on neuropathological and neurochemical changes in a mouse model of Alzheimer's disease

Interest in brain-derived neurotrophic factor (BDNF) was greatly enhanced when it was recognized that its expression is reduced in neurodegenerative disorders, especially in Alzheimer's disease (AD). BDNF signaling through the TrkB receptor has a central role in promoting synaptic transmission, synaptogenesis, and facilitating synaptic plasticity making the BDNF-TrkB signaling pathway an attractive candidate for targeted therapies. Here we investigated the early effect of the small molecule TrkB agonist, 7,8 dihydroxyflavone (7,8-DHF), on AD-related pathology, dendritic arborization, synaptic density, and neurochemical changes in the 5xFAD mouse model of AD. We treated 5xFAD mice with 7,8-DHF for 2 months beginning at 1 month of age. We found that, in this model of AD, 7,8-DHF treatment decreased cortical Aβ plaque deposition and protected cortical neurons against reduced dendritic arbor complexity but had no significant impact on the density of dendritic spines. In addition 7,8-DHF treatment protected against hippocampal increase in the level of choline-containing compounds and glutamate loss, but had no significant impact on hippocampal neurogenesis.

The effects of aging, housing and ibuprofen treatment on brain neurochemistry in a triple transgene Alzheimer's disease mouse model using magnetic resonance spectroscopy and imaging

We investigated a triple transgene Alzheimer's disease (AD) mouse model that recapitulates many of the neurochemical, anatomic, pathologic and behavioral defects seen in human AD. We studied the mice as a function of age and brain region and investigated potential therapy with the non-steroidal anti-inflammatory drug ibuprofen. Magnetic resonance spectroscopy (MRS) showed alterations characteristic of AD (i.e. increased myo-inositol and decreased N-acetylaspartate (NAA)). Mice at 6 months of age showed an increase in myo-inositol in the hippocampus at a time when the Aβ is intracellular, but not in amygdala or cortex. Myo-inositol increased as a function of age in the amygdala, cortex and striatum while NAA decreased only in the hippocampus and cortex at 17-23 months of age. Ibuprofen protected the increase of myo-inositol at six months of age in the hippocampus, but had no effect at 17-23 months of age (a time when Aβ is extracellular). In vivo MRI and MRS showed that at 17-23 months of age there was a significant protective effect of ibuprofen on hippocampal volume and NAA loss. Together, these data show the following: the increase in myo-inositol occurs before the decrease in NAA in hippocampus but not cortex; the hippocampus shows earlier changes than does the amygdale or cortex consistent with earlier deposition of Aβ40-42 in the hippocampus and ibuprofen protects against multiple components of the AD pathology. These data also show a profound effect of housing on this particular mouse model.

Pathophysiological rat model of vascular dementia: magnetic resonance spectroscopy, microimaging and behavioral study

Chronic cerebral hypoperfusion and aging can be related to vascular dementia manifested by the decline in cognitive abilities and memory impairment. The identification of specific biomarkers of vascular disorder in early stages is important for the development of neuroprotective agents. In the present study, a three-vessel occlusion (3-VO) rat model of vascular dementia in the middle-aged rat brain was used to investigate the effect of global cerebral hypoperfusion. A multimodal study was performed using magnetic resonance spectroscopy, MR-microimaging, histology and behavioral tests. Our measurements showed a signal alteration in T2-weighted MR images, the elevation of T2 relaxation times and histologically proven neural cell death in the hippocampal area, as well as mild changes in concentration of proton and phosphorus metabolites. These changes were accompanied by mild behavioral alterations in the open field and slightly decreased habituation. The analysis of the effects of vascular pathology on cognitive functions and neurodegeneration can contribute to the development of new treatment strategies for early stages of neurodegeneration.

R-flurbiprofen improves tau, but not Aß pathology in a triple transgenic model of Alzheimer's disease

We have previously reported that chronic ibuprofen treatment improves cognition and decreases intracellular Aß and phosphorylated-tau levels in 3xTg-AD mice. Ibuprofen is a non-steroidal anti-inflammatory drug (NSAID) that independently of its anti-inflammatory effects has anti-amyloidogenic activity as a gamma-secretase modulator (GSM) and both activities have the potential to decrease Aß pathology. To further understand the effects of NSAIDs in 3xTg-AD mice, we treated 3xTg-AD mice with R-flurbiprofen, an enantiomer of the NSAID flurbiprofen that maintains the GSM activity but has greatly reduced anti-inflammatory activity, and analyzed its effect on cognition, Aß, tau, and the neurochemical profile of the hippocampus. Treatment with R-flurbiprofen from 5 to 7 months of age resulted in improved cognition on the radial arm water maze (RAWM) test and decreased the level of hyperphosphorylated tau immunostained with AT8 and PHF-1 antibodies. No significant changes in the level of Aß (using 6E10 and NU-1 antibodies) were detected. Using magnetic resonance spectroscopy (MRS) we found that R-flurbiprofen treatment decreased the elevated level of glutamine in 3xTg-AD mice down to the level detected in non-transgenic mice. Glutamine levels correlated with PHF-1 immunostained hyperphosphorylated tau. We also found an inverse correlation between the concentration of glutamate and learning across all the mice in the study. Glutamine and glutamate, neurochemicals that shuttles between neurons and astrocytes to maintain glutamate homeostasis in the synapses, deserve further attention as MR markers of cognitive function.

Metabolomics as a tool for personalizing medicine: 2012 update

Numerous factors in conjunction with an individual’s genetic make up will determine predisposition to disease, adverse or beneficial effects of drug treatment or therapy, and disease progression. A major limitation of current clinical measures is that the disease phenotype, which is comprised of the genotype and other environmental factors, is underestimated. Rather, each disease is treated similarly even though the disease process is highly complex. Methods that evaluate the interaction of genotype and environmental factors would likely be a better indicator of patients’ response to medical treatments. The omics technologies, specifically metabolomics, will play a major role in the movement towards personalized medicine. Metabolomics is phenotype driven and should provide better clinical biomarkers. Furthermore, recent studies have shown that associations between genetic variants and downstream metabolite changes can provide a unique description of an individual’s genotype and phenotype, which will further enhance the movement towards personalized medicine.

Iron supplementation dose for perinatal iron deficiency differentially alters the neurochemistry of the frontal cortex and hippocampus in adult rats

BACKGROUND

Long-term prefrontal cortex (PFC)- and hippocampus-based cognitive deficits are the sequelae of perinatal iron deficiency, despite iron supplementation starting in the newborn period. Whether high-dose iron supplementation prevents these deficits is yet to be determined.

METHODS

Perinatal iron deficiency was induced in rat pups using a low-iron (3 mg/kg diet) diet during gestation until postnatal day (P)8. Iron was supplemented using a standard (40 mg/kg diet) or a 10-fold higher (400 mg/kg diet) iron-containing diet until P21. PFC and hippocampal neurochemistry was determined using in vivo (1)H nuclear magnetic resonance (NMR) spectroscopy at 9.4 Tesla on P90.

RESULTS

Both standard and 10-fold higher iron supplementation doses corrected anemia and brain iron deficiency by P21. The neurochemical profile of the PFC in both supplementation groups was comparable with the control group. In the hippocampus, standard-dose iron supplementation resulted in lower concentrations of N-acetylaspartate (NAA) and phosphoethanolamine (PE) and higher concentrations of N-acetylaspartylglutamate (NAAG) and glycerophosphocholine + phosphocholine (GPC + PC). High-dose iron supplementation resulted in lower PE and higher GPC + PC concentrations.

CONCLUSION

The iron supplementation dose for perinatal iron deficiency differentially alters the neurochemical profile of the PFC and hippocampus in adults. The neurochemical changes suggest altered glutamatergic neurotransmission, hypomyelination, and abnormal phospholipid metabolism in the formerly iron-deficient (FID) hippocampus.

The heritability of brain metabolites on proton magnetic resonance spectroscopy in older individuals

Twin studies have shown that many aspects of brain structure are heritable, suggesting a strong genetic contribution to brain structure. Less is known about functional aspects of the brain, in particular biologically relevant metabolites in the brain such as those measured by proton magnetic resonance spectroscopy (((1))H MRS), N-acetyl-aspartate (NAA), creatine (Cr), choline (Cho) and myoinositol (ml), which have been suggested as possible markers of brain aging and early dementia. We examined 296 (56 male/108 female monozygotic and 43 male/89 female dizygotic) older twins (mean age 72.2 ± 5.5 years, range 65-88), for the levels of these metabolites relative to the H(2)O signal in the posterior cingulate cortex using ((1))H MRS. All metabolites showed substantial heritability, which was greatest for the neuronal integrity marker NAA (72%), and less so for the others - Cr (51%), Cho (33%) and ml (55%). The heritability of these markers did not change significantly with age or sex. The genetic determination of NAA, along with the evidence that NAA levels change in aging and neurodegenerative diseases suggest that it is a potential endophenotype of brain aging and dementia.

Detection of increased scyllo-inositol in brain with magnetic resonance spectroscopy after dietary supplementation in Alzheimer's disease mouse models

There is evidence that inositol isomers may help protect against formation of toxic fibrils of Abeta fragments in Alzheimer's disease mouse models. Scyllo-inositol is one of the more promising inositol isomers for the potential treatment of Alzheimer's disease (AD) and can be detected using MRS in human subjects. In this manuscript we demonstrate using MRS, in two different mouse models of AD (APP x PS1 and APP x PS1 x tau), that we could detect increased scyllo-inositol in the hippocampus and frontal cortex in mice fed water supplemented with 16.5 mg/L of scyllo-inositol equivalent to about 3.3 mg/kg/day. We used both brain extracts using solution MRS as well as intact brain tissue using high resolution magic angle spinning (HRMAS) to ensure that any membrane-associated scyllo-inositol would be detected. By brain extracts we detected a 3.0 fold increase in scyllo-inositol in the scyllo-fed AD mice compared to normal diet (p < 0.001). Using HRMAS we detected a 2.2-2.4-fold increase in scyllo-inositol (p < 0.001). Scyllo-inositol treatment was associated with an increase in glutamine in hippocampus. The concentrations of scyllo-inositol were higher in the hippocampus than in the frontal cortex. Mice have a smaller concentration of scyllo-inositol than humans (ca. 100 microM vs. 500 microM in humans). Given the ease with which scyllo-inositol can be measured in human MRS data with high signal to noise ratios, these data suggest that MRS will prove useful for evaluation of inositol treatment trials in AD subjects.

Advanced In Vivo Heteronuclear MRS Approaches for Studying Brain Bioenergetics Driven by Mitochondria

The greatest merit of in vivo magnetic resonance spectroscopy (MRS) methodology used in biomedical research is its ability for noninvasively measuring a variety of metabolites inside a living organ. It, therefore, provides an invaluable tool for determining metabolites, chemical reaction rates and bioenergetics, as well as their dynamic changes in the human and animal. The capability of in vivo MRS is further enhanced at higher magnetic fields because of significant gain in detection sensitivity and improvement in the spectral resolution. Recent progress of in vivo MRS technology has further demonstrated its great potential in many biomedical research areas, particularly in brain research. Here, we provide a review of new developments for in vivo heteronuclear 31P and 17O MRS approaches and their applications in determining the cerebral metabolic rates of oxygen and ATP inside the mitochondria, in both animal and human brains.

Alzheimer's disease beyond the genomic era: nuclear magnetic resonance (NMR) spectroscopy-based metabolomics

Alzheimer's disease (AD) is a complex disease, with no definitive biomarkers available that allow clinical diagnosis; this represents a major problem for the advance of efficient drug discovery programs. A successful approach towards the understanding and treatment of AD should take into consideration this complex nature. In this sense, metabolic networks are subject to severe stoichiometric restrictions. Metabolomics amplifies changes both in the proteome and the genome, and represents a more accurate approximation to the phenotype of an organism in health and disease. In this article, we will examine the current rationale for metabolomics in AD, its basic methodology and the available data in animal models and human studies. The discussed topics will highlight the importance of being able to use the metabolomic information in order to understand disease mechanisms from a systems biology perspective as a non-invasive approach to diagnose and grade AD. This could allow the assessment of new therapies during clinical trials, the identification of patients at risk to develop adverse effects during treatment and the final implementation of new tools towards a more personalized medicine.

Application of MRS to mouse models of neurodegenerative illness

The rapid development of transgenic mouse models of neurodegenerative diseases, in parallel with the rapidly expanding growth of MR techniques for assessing in vivo, non-invasive, neurochemistry, offers the potential to develop novel markers of disease progression and therapy. In this review we discuss the interpretation and utility of MRS for the study of these transgenic mouse and rodent models of neurodegenerative diseases such as Alzheimer's (AD), Huntington's (HD) and Parkinson's disease (PD). MRS studies can provide a wealth of information on various facets of in vivo neurochemistry, including neuronal health, gliosis, osmoregulation, energy metabolism, neuronal-glial cycling, and molecular synthesis rates. These data provide information on the etiology, natural history and therapy of these diseases. Mouse models enable longitudinal studies with useful time frames for evaluation of neuroprotection and therapeutic interventions using many of the potential MRS markers. In addition, the ability to manipulate the genome in these models allows better mechanistic understanding of the roles of the observable neurochemicals, such as N-acetylaspartate, in the brain. The argument is made that use of MRS, combined with correlative histology and other MRI techniques, will enable objective markers with which potential therapies can be followed in a quantitative fashion.

[Proton spectroscopy in Alzheimer's disease and cognitive impairment not dementia: a community study]

OBJECTIVE

To describe the proton magnetic resonance spectroscopy (1H-ERM) data in Alzheimer's disease (AD) and Cognitive Impairment Not Dementia (CIND) in a community sample.

METHOD

We investigated subjects with AD (n=6), CIND (n=7) and normal control (n=7). 1H-ERM was performed with single voxel (8 cm3) placed in temporal, parietal and occipital regions and studied metabolites were: N-acetylaspartate (NAA), creatine (Cr), choline (Cho) and myo-inositol (mI).

RESULTS

NAA concentration was higher in control subjects than AD and intermediated in CIND patients. Cho parietal plus occipital and Cr parietal plus Cho occipital classified correctly 92.3% of subjects Control vs AD. Temporal mI classified 78.6% of subjects between Control vs CIND.

CONCLUSION

Spectroscopy can be used in the diagnosis and follow-up of individuals with cognitive impairment; evaluation of community subjects may show different patterns of brain metabolites distribution.

Detection of age-dependent brain injury in a mouse model of brain amyloidosis associated with Alzheimer's disease using magnetic resonance diffusion tensor imaging

Using magnetic resonance diffusion tensor imaging (DTI), the present study investigates changes in both gray and white matter in the APPsw transgenic mouse (Tg2576), a model of beta-amyloid plaque deposition associated with Alzheimer's disease (AD). DTI analyses were performed in cross-sectional groups of transgene-positive and -negative mice at 8, 12, 16, and 18 months of age to assess the magnitude of water diffusion in gray matter (i.e., Tr(D)) and changes in diffusion in white matter that may be indicative of axonal degeneration (i.e., reduced water diffusion parallel to axonal tracts, lambda(||)) and myelin degradation (i.e., increased water diffusion perpendicular to axonal tracts, lambda(perpendicular)). No appreciable changes in gray or white matter were observed between the APPsw and the age-matched control mice at 8 months of age. Reduced Tr(D) and lambda(||) were observed in gray and white matter, respectively, for the APPsw mice at ages greater than 8 months, which coincides with the time period when appreciable amyloid plaque accumulation was confirmed by ex vivo histopathological studies. The decreases in lambda(||) suggest the presence of axonal injury in multiple white matter tracts of APPsw mice. Unlike lambda(||), lambda(perpendicular) was unaltered between control and APPsw mice in most white matter tracts. However, in the corpus collosum (CC), lambda(perpendicular) increased at 16 and 18 months of age, suggesting the possibility of myelin damage in the CC at these later ages. This work demonstrates the potential for DTI as a noninvasive modality to detect evolving pathology associated with changes in tissue water diffusion properties in brain tissues.

Molecular Causes of the Aberrant Choline Phospholipid Metabolism in Breast Cancer

Proton magnetic resonance spectroscopy ((1)H MRS) consistently detects significant differences in choline phospholipid metabolites of malignant versus benign breast lesions. It is critically important to understand the molecular causes underlying these metabolic differences, because this may identify novel targets for attack in cancer cells. In this study, differences in choline membrane metabolism were characterized in breast cancer cells and normal human mammary epithelial cells (HMECs) labeled with [1,2-(13)C]choline, using (1)H and (13)C magnetic resonance spectroscopy. Metabolic fluxes between membrane and water-soluble pool of choline-containing metabolites were assessed by exposing cells to [1,2-(13)C]choline for long and short periods of time to distinguish between catabolic and anabolic pathways in choline metabolism. Gene expression analysis using microarrays was performed to understand the molecular mechanisms underlying these changes. Breast cancer cells exhibited increased phosphocholine (PC; P < 0.001), total choline-containing metabolites (P < 0.01), and significantly decreased glycerophosphocholine (P < 0.05) compared with normal HMECs. Decreased (13)C-enrichment was detected in choline (P < 0.001) and phosphocholine (P < 0.05, P < 0.001) of breast cancer cells compared with HMECs, indicating a higher metabolic flux from membrane phosphatidylcholine to choline and phosphocholine in breast cancer cells. Choline kinase and phospholipase C were significantly overexpressed, and lysophospholipase 1, phospholipase A2, and phospholipase D were significantly underexpressed, in breast cancer cells compared with HMECs. The magnetic resonance spectroscopy data indicated that elevated phosphocholine in breast cancer cells was primarily attributable to increased choline kinase activity and increased catabolism mediated by increased phospholipase C activity. These observations were consistent with the overexpression of choline kinase and phospholipase C detected in the microarray analyses.

Imaging the pathology of Alzheimer's disease: amyloid-imaging with positron emission tomography

The steep rise in the incidence of Alzheimer's disease (AD) has further added to the considerable public health burden caused by aging of the United States population. Among the most characteristic pathologic hallmarks of AD are neuritic plaques and neurofibrillary tangles. The capability to use positron emission tomography and selective markers for amyloid protein deposition promises to substantially alter the way we diagnosis and manage patients who have AD.

Dietary lipids in the aetiology of Alzheimer's disease: implications for therapy

Amyloid plaques and neurofibrillary tangles are the neuropathological hallmarks of Alzheimer's disease (AD), but no conclusive evidence has emerged showing that these hallmarks are the cause and not a product of the disease. Many studies have implicated oxidation and inflammation in the AD process, and there is growing evidence that abnormalities of lipid metabolism also play a role. Using epidemiology to elucidate risk factors and histological changes to suggest possible mechanisms, the hypothesis is advanced that dietary lipids are the principal risk factor for the development of late-onset sporadic AD. The degree of saturation of fatty acids and the position of the first double bond in essential fatty acids are the most critical factors determining the effect of dietary fats on the risk of AD, with unsaturated fats and n-3 double bonds conferring protection and an overabundance of saturated fats or n-6 double bonds increasing the risk. The interaction of dietary lipids and apolipoprotein E isoforms may determine the risk and rate of sustained autoperoxidation within cellular membranes and the efficacy of membrane repair. Interventions involving dietary lipids and lipid metabolism show great promise in slowing or possibly averting the development of AD, including dietary changes, cholesterol-modifying agents and antioxidants.

MR spectroscopy in Alzheimer's disease: gender differences in probabilistic learning capacity

Degenerative alterations of cortical and subcortical regions in Alzheimer disease (AD) can be estimated by the extent of brain metabolite changes as measured by magnetic resonance spectroscopic imaging (MRSI). A neuropsychological assessment may correlate with metabolite levels and could evaluate underlying degenerative processes. Probabilistic-related classification learning, which represents one form of procedural learning, is associated with the neostriatum. The present study was aimed at examining the correlation of spectroscopic imaging in subcortical regions with the evaluation of specific neuropsychological findings. Twenty-two patients with Alzheimer's disease were compared to 15 healthy elderly control subjects. Proton MRSI of the basal ganglia (BG) and thalamus region was performed for detection of N-acetylaspartate (NAA), trimethylamine (TMA) and creatine ((P)Cr). In addition, a probabilistic-related classification learning task (Weather Prediction Task (WT)) was applied. We observed that in patients a high TMA signal in the basal ganglia region was correlated with a poorer performance in the probabilistic learning task (Spearman rank order correlation (SROC)=-0.6, P<0.009). Although Alzheimer's patients, as a group, did not differ from controls with regard to probabilistic learning capacity (PLC), male AD patients, as compared to male controls, displayed an impairment in the task performance by 28% (P<0.03) and showed a 16% elevation in TMA signaling (P<0.04). The altered metabolite signals and ratios in combination with the cognitive performance might suggest gender-related neuronal degeneration and dysfunction within subcortical regions in AD.

Magnetic resonance spectroscopy and cognitive function in healthy elderly men

Subtle cognitive decrements in older people are important in terms of the associated morbidity and as a risk factor for dementia. However, their pathophysiological basis is poorly understood. Proton magnetic resonance spectroscopy ((1)H-MRS) may provide the means to investigate early changes in brain metabolite concentrations. We examined the relationships between N-acetylaspartate (NAA), choline (Cho) and creatine (Cr) metabolite ratios in a voxel in the parietal cortex and cognitive function in 88 healthy, non-demented, unmedicated men aged 65-70 years. We also used linear regression to give a value for each metabolite adjusted for the levels of the other two metabolites. Both NAA/Cr and Cho/Cr ratios correlated positively with tests of verbal memory and a verbal memory factor (e.g. NAA/Cr and Logical Memory: r = 0.24, P < 0.05). Cho/Cr ratios also correlated positively with tests of visual memory (e.g. visual reproduction: r = 0.21, P < 0.05). Adjusted Cr levels correlated negatively and significantly with tests of verbal memory and the Verbal Memory Factor. The regression analysis suggested that Cr levels better explained the correlations between NAA/Cr and Cho/Cr ratios and cognitive variables than NAA or Cho levels. These results suggest that in healthy men aged 65-70 years, metabolite levels relate to cognitive performance. Rising Cr levels may be an early marker of cognitive decline.

Ammonia and Alzheimer's disease

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder. Behavioural, cognitive and memory dysfunctions are characteristic symptoms of AD. The formation of amyloid plaques is currently considered as the key event of AD. Other histological hallmarks of the disease are the formation of fibrillary tangles, astrocytosis, and loss of certain neuronal systems in cortical areas of the brain. A great number of possible aetiologic and pathogenetic factors of AD have been published in the course of the last two decades. Among the toxic factors, which have been considered to contribute to the symptoms and progression of AD, ammonia deserves special interest for the following reasons: (a) Ammonia is formed in nearly all tissues and organs of the vertebrate organism; it is the most common endogenous neurotoxic compounds. Its effects on glutamatergic and GABAergic neuronal systems, the two prevailing neuronal systems of the cortical structures, are known for many years. (b) The impairment of ammonia detoxification invariably leads to severe pathology. Several symptoms and histologic aberrations of hepatic encephalopathy (HE), of which ammonia has been recognised as a pathogenetic factor, resemble those of AD. (c) The excessive formation of ammonia in the brains of AD patients has been demonstrated, and it has been shown that some AD patients exhibit elevated blood ammonia concentrations. (d) There is evidence for the involvement of aberrant lysosomal processing of beta-amyloid precursor protein (beta-APP) in the formation of amyloid deposits. Ammonia is the most important natural modulator of lysosomal protein processing. (e) Inflammatory processes and activation of microglia are widely believed to be implicated in the pathology of AD. Ammonia is able to affect the characteristic functions of microglia, such as endocytosis, and cytokine production. Based on these facts, an ammonia hypothesis of AD has first been suggested in 1993. In the present review old and new observations are discussed, which are in support of the notion that ammonia is a factor able to produce symptoms of AD and to affect the progression of the disease.

Brain membrane phospholipid alterations in Alzheimer's disease

Studies have demonstrated alterations in brain membrane phospholipid metabolite levels in Alzheimer's disease (AD). The changes in phospholipid metabolite levels correlate with neuropathological hallmarks of the disease and measures of cognitive decline. This 31P nuclear magnetic resonance (NMR) study of Folch extracts of autopsy material reveals significant reductions in AD brain levels of phosphatidylethanolamine (PtdEtn) and phosphatidylinositol (PtdIns), and elevations in sphingomyelin (SPH) and the plasmalogen derivative of PtdEtn. In the superior temporal gyrus, there were additional reductions in the levels of diphosphatidylglycerol (DPG) and phosphatidic acid (PtdA). The findings are present in 3/3 as well as 3/4 and 4/4 apolipoprotein E (apoE) genotypes. The AD findings do not appear to reflect non-specific neurodegeneration or the presence of gliosis. The present findings could possibly contribute to an abnormal membrane repair in AD brains which ultimately results in synaptic loss and the aggregation of A beta peptide.

Postprocessing method to segregate and quantify the broad components underlying the phosphodiester spectral region of in vivo (31)P brain spectra

In a typical, in vivo (31)P brain spectrum, the phosphomonoester (PME) and phosphodiester (PDE) spectral region not only contains signals from freely mobile PMEs and PDEs (which are anabolic and catabolic products of membrane phospholipids) but also signals of broader underlying lineshapes from less-mobile molecules. In general, either the PME and PDE resonances are quantified as a combined value of freely mobile metabolites plus less-mobile molecules or the broader underlying signal is reduced/eliminated prior to or post data collection. In this study, a postprocessing method that segregates and quantifies the individual contributions of the freely mobile metabolites and the less-mobile molecules is introduced. To demonstrate the precision and accuracy of the method, simulated data and in vivo (31)P brain spectroscopy data of healthy individuals were quantified. The ability to segregate and quantify these various PME and PDE contributions provides additional spectral information and improves the accuracy of the interpretation of (31)P spectroscopy results. Magn Reson Med 45:390-396, 2001.

Magnetic resonance imaging and magnetic resonance spectroscopy in dementias

This article reviews recent studies of magnetic resonance imaging and magnetic resonance spectroscopy in dementia, including Alzheimer's disease, frontotemporal dementia, dementia with Lewy bodies, idiopathic Parkinson's disease, Huntington's disease, and vascular dementia. Magnetic resonance imaging and magnetic resonance spectroscopy can detect structural alteration and biochemical abnormalities in the brain of demented subjects and may help in the differential diagnosis and early detection of affected individuals, monitoring disease progression, and evaluation of therapeutic effect.

Acceleration of phosphatidylcholine synthesis and breakdown by inhibitors of mitochondrial function in neuronal cells: a model of the membrane defect of Alzheimer's disease

Brain cells in Alzheimer's disease (AD) exhibit a membrane defect characterized by accelerated phospholipid turnover. The mechanism responsible for this defect remains unknown. Recent studies indicate that impairment of mitochondrial function is frequently observed in AD and may be responsible for certain aspects of its pathophysiology. We show that when PC12 cells are exposed to inhibitors of mitochondrial bioenergetics, the turnover of their major membrane phospholipid, phosphatidylcholine, is accelerated, producing a pattern of metabolic changes that mimics that observed in brains of AD patients. Abnormalities of mitochondrial function may therefore underlie the membrane defect in AD.

Molecular insights into neurodevelopmental and neurodegenerative diseases

Magnetic resonance spectroscopy (MRS) is a non-invasive physical technique that is routinely used to determine the quantity and structure of organic molecules in solution. Technical advances that have expanded the usefulness of this technique include: (1) high resolution MRS to identify and quantify individual molecules present in complex mixtures of tissue extracts; (2) in vivo MRS techniques to non-invasively monitor metabolites in humans; (3) structure determination of proteins of moderate size; and (4) improved structure characterization of solids and liquid crystals, such as the detection of phase changes in membranes. The focus of this review is on the first two technical advances mentioned above. The strengths of MRS as a research tool to investigate molecular alterations in disease states include ease of sample preparation, minimum sample manipulation, avoidance of the preparation of derivatives, and the ability to analyze an unfractionated sample. The strengths of MRS in the clinic are its ability to measure neuronal metabolite levels non-invasively in humans and its potential for disease diagnosis, monitoring disease progression, and assessing the efficacy of experimental therapies.

A frontal variant of Alzheimer's disease exhibits decreased calcium-independent phospholipase A2 activity in the prefrontal cortex

A frontal variant of Alzheimer's disease (AD) has recently been identified on neuropathological and neuropsychological grounds (Johnson, J.K., Head, E., Kim, R., Starr, A., Cotman, C.W., 1999. Clinical and pathological evidence for a frontal variant of Alzheimer Disease. Arch. Neurol. 56, 1233-1239). Frontal AD differs strikingly from typical AD by the occurrence of neurofibrillary tangle densities in the frontal cortex as high or higher than in the entorhinal cortex. Since cerebrocortical membranes are commonly abnormal in Alzheimer's disease (AD), we assayed frontal AD cases for enzymes regulating membrane phospholipid composition. We specifically measured activity of phospholipase A2s (PLA2s) in dorsolateral prefrontal and lateral temporal cortices of frontal AD cases (n=12), which have respectively high and low densities of neurofibrillary tangles. In neither cortical area was Ca(2+)-dependent PLA2 activity abnormal compared to controls (n=12). In contrast, a significant 42% decrease in Ca(2+)-independent PLA2 activity was found in the dorsolateral prefrontal, but not the lateral temporal, cortex of the frontal AD cases. Similarly, the dorsolateral prefrontal cortex, but not the lateral temporal cortex of the frontal AD cases suffered a 42% decrease in total free fatty acid content, though neither that decrease nor those in any one species of free fatty acid was significant. The observed biochemical changes probably occurred in neurons given (a) our finding that PLA2 activity of cultured human NT2 neurons is virtually all Ca(2+)-independent and (b) the finding of others that nearly all Ca(2+)-independent PLA2 in brain gray matter is neuronal. The decrease in Ca(2+)-independent PLA2 activity is not readily attributable to Group VI or VIII iPLA2s since neither NT2N neurons nor our brain homogenates were greatly inhibited by drugs potently suppressing those iPLA2s. Decreased Ca(2+)-independent PLA2 activity in frontal AD may reflect a compensatory response to pathologically accelerated phospholipid metabolism early in the disorder. That could cause an early elevation of prefrontal free fatty acids, which can stimulate polymerization of tau and thus promote the prefrontal neurofibrillary tangle formation characteristic of frontal AD.

An integrated strategy for evaluation of metabolic and oxidative defects in neurodegenerative illness using magnetic resonance techniques

The number of physiologic and metabolic phenomena amenable to analysis using magnetic resonance (MR) techniques is increasing every year. MR techniques can now evaluate tissue parameters relevant to TCA cyclemetabolism, anerobic glycolysis, ATP levels, blood-brain barrier permeability, macrophage infiltration, cytotoxic edema, spreading depression, cerebral blood flow and volume, and neurotransmitter function. The paramagnetic nature of certain oxidation states of iron leads to the ability to map out brain function using deoxyhemoglobin as an endogenous contrast agent, and also allows for mapping of local tissue iron concentrations. In addition to these metabolic parameters, the number of ways to generate anatomic contrast using MR is also expanding; and in addition to conventional anatomic scans, mapping of axonal fiber tracts can also be performed using the anisotropy of water diffusion. A strategy for integration of these multifarious parameters in a comprehensive neurofunctional exam in neurodegenerative illness is outlined in this paper. The goals of the integrated exam, as applied to a given neurodegenerative illness, can be subdivided into three categories: etiology, natural history, and therapeutic end points. The consequences of oxidative stress and/or mitochondrial dysfunction are explored in the context of the various parameters that can be measured using the integrated MR exam.

Increased cerebral cortical lipid peroxidation and abnormal phospholipids in aged homozygous apoE-deficient C57BL/6J mice

Aged homozygous apolipoprotein E gene-deficient (apoE -/-) mice have been proposed as an experimental model for the role of human apoE isoforms in Alzheimer's disease (AD). However, results from different laboratories have been in conflict regarding the presence or absence of neurodegeneration in these mice. Moreover, despite apoE being the major lipid trafficking molecule in the central nervous system, there has been no investigation of brain lipid levels in apoE -/- mice. Here we have examined male and female apoE -/- and control mice aged 10 to 12 months, testing the hypothesis that lack of apoE leads to some of the neuropathological changes seen in AD. Our results failed to demonstrate significant neurodegeneration, histopathological changes, or reduction in cerebral cortical synaptophysin in apoE -/- mice. However, we did observe a significant reduction in cerebral cortical phospholipids and their constituent fatty acids, as well as elevated lipid peroxidation products, in apoE -/- mice compared to apoE +/+ mice with the same genetic background. Our results suggest that the brains of aged apoE -/- mice display some of the lipid abnormalities associated with AD; however, these changes alone, at the magnitudes achieved in the apoE -/- mice, do not directly lead to the major neurodegenerative changes of AD.